a big meal + stress could cause the anemone to split but usually it takes a little time , like 1 to 3 days, for a big anemone to split. A healthy anemone should have a big fat cylinder foot/trunk with no exposed white stuff be it in the foot or mouth.
If you see that in the anemone, just say deal off. I dont know either party so just from what I see in my anemones.
Hopefully you/seller can work out something but hopefully it could make it Jimmy. One of my almost 10" sherman anemone decided to pull itself through a 1/4" gap and shredded really bad but it recovered. Give it some TLC